The present invention relates, in general, to measurement systems and, more particularly, to the measurement systems for electrical signals.
Circuits for measuring or calculating electrical signals such as current, voltage, and power and circuits for measuring or calculating electrical parameters such as impedance, admittance, phase relationships are used in a variety of applications including impedance measurements, load detection and calibration, security systems, smart grids, sensor interfaces, automotive systems, self-test systems, etc. For example, circuits used for determining the impedance of a system may include a resistor placed in series with a load so that the current flowing through the resistor can be used to determine the current flowing through the load. Drawbacks with this technique are the reduction of the input voltage range, the consumption of large areas of semiconductor material to manufacture the circuits, frequency limitations of the circuit elements, and the need for highly accurate circuit elements.
In some applications it may be desirable to detect a ground fault condition. One technique for detecting this condition is to establish resonance in an inductor-resistor-capacitor network when it is exposed to a ground-to-neutral condition. Resonance may be established by delivering a pulse to a positive feedback system that includes an operational amplifier. Alternatively, a steady state stimulus can be delivered to the circuit, which is then monitored for significant changes in the waveform profile. Drawbacks with these techniques are that they are prone to temperature and manufacturing shifts which reduce the accuracy of detection.
Accordingly, it would be advantageous to have a circuit and method for determining electrical signals and electrical parameters of a circuit element. It would be of further advantage for the circuit and method to be cost efficient to implement.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or an anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain n-channel or p-channel devices, or certain n-type or p-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action and the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten per cent (10%) (and up to twenty per cent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of exactly as described.
It should be noted that a logic zero voltage level (VL) is also referred to as a logic low voltage or logic low voltage level and that the voltage level of a logic zero voltage is a function of the power supply voltage and the type of logic family. For example, in a Complementary Metal Oxide Semiconductor (CMOS) logic family a logic zero voltage may be thirty percent of the power supply voltage level. In a five volt Transistor-Transistor Logic (TTL) system a logic zero voltage level may be about 0.8 volts, whereas for a five volt CMOS system, the logic zero voltage level may be about 1.5 volts. A logic one voltage level (VH) is also referred to as a logic high voltage level, a logic high voltage, or a logic one voltage and, like the logic zero voltage level, the logic high voltage level also may be a function of the power supply and the type of logic family. For example, in a CMOS system a logic one voltage may be about seventy percent of the power supply voltage level. In a five volt TTL system a logic one voltage may be about 2.4 volts, whereas for a five volt CMOS system, the logic one voltage may be about 3.5 volts.